N-substituted azaheterocyclic carboxylic acids and esters thereof

ABSTRACT

The present invention relates to therapeutically active azaheterocyclic compounds, a method of preparing the same and to pharmaceutical compositions comprising the compounds. The novel compounds are useful in treating a central nervous system ailment related to the GABA uptake.

FIELD OF THE INVENTION

The present invention relates to novel N-substituted azaheterocycliccarboxylic acids and esters thereof in which a substituted alkyl chainforms part of the N-substituent and salts thereof, to methods for theirpreparation, to compositions containing them, and to their use for theclinical treatment of abnormal function of the γ-aminobutyric acidneurotransmission system.

BACKGROUND OF THE INVENTION

In recent years much pharmacological research concerning γ-aminobutyricacid (hereinafter designated GABA), an inhibitory neurotransmitter inthe mammalian central nervous system, has been carried out.

The inhibition of GABA uptake results in enhanced availability of thisinhibitory neurotransmitter in the synaptic cleft and thus to increasedGABA'ergic activity. Increased GABA'ergic activity can be useful in thetreatment, for example of anxiety, pain and epilepsy, as well asmuscular and movement disorders (see, for example, P. Krogsgaard-Larsenet al., Progress in Medicinal Chemistry, 1985, 22, 68-112).

A well-known and potent inhibitor of GABA uptake from the synaptic cleftinto presynaptic nerve terminals and glial cells is, for example,3-piperidine-carboxylic acid (nipecotic acid). However, being arelatively compound and therefore unable to cross the blood-brainbarrier, 3-piperidine-carboxylic acid itself has found no practicalutility as a drug.

In U.S. Pat. No. 4,383,999 and 4,514,414 and in EP 236342 as well as inEP 231996 some derivatives ofN-(4,4-disubstituted-3-butenyl)azahetero-cyclic carboxylic acids areclaimed as inhibitors of GABA uptake. In EP 342635 and EP 374801,N-substituted azaheterocyclic carboxylic acids in which an oxime ethergroup and vinyl ether group forms part of the N-substituent respectivelyare claimed as inhibitors of GABA uptake. Further, in WO 9107389 and WO9220658, N-substituted azacyclic carboxylic acids are claimed asinhibitors of GABA uptake. EP 221572 claims that1-aryl-oxyalkylpyridine-3-carboxylic acids are inhibitors of GABAuptake.

According to Yunger, L. M. et al., J. Pharm. Exp. Ther. 1984, 228, 109,N-(4,4-diphenyl-3-buten-1-yl)nipecotic acid (designated SK&F 89976A),N-(4,4-diphenyl-3-buten-1-yl)guvacine (designated SK&F 100330A),N-(4,4-diphenyl-3-buten-1-yl)-homo-β-proline (designated SK&F 100561)and N-(4-phenyl-4-(2-thienyl)-3-buten-1-yl)nipecotic acid (designatedSK&F 100604J) are orally active inhibitors of GABA uptake. These dataare summarized in Krogsgaard-Larsen, P. et al., Epilepsy Res. 1987, 1,77-93.

DESCRIPTION OF THE INVENTION

The present invention relates to novel N-substituted azaheterocycliccarboxylic acids and esters thereof of formula I ##STR1## wherein A is asaturated or unsaturated five or six-membered carbocyclic ringoptionally substituted with a phenyl, benzylidene, C₁₋₄ -alkylsubstituted with phenyl or C₂₋₄ -alkenyl substituted with phenyl whichphenyl or benzylidene is optionally substituted with halogen, C₁₋₄-alkyl, C₁₋₄ -alkoxy or trifluoromethyl and which saturated orunsaturated five or six-membered carbocyclic ring may be optionallyfused with a benzo ring;

R¹ and R² represent hydrogen or may together represent a bond;

X is hydroxy or C₁₋₄ -alkoxy;

n is 1, 2, 3, 4 or 5; or a pharmaceutically acceptable salt thereof.

The compounds of formula I may exist as geometric and optical isomersand all isomers and mixtures thereof are included herein. Isomers may beseparated by means of standard methods such as chromatographictechniques or fractional crystallisation of suitable salts.

The compounds according to the invention may optionally exist aspharmaceutically acceptable acid addition salts or--when the carboxylicacid group is not esterified--as pharmaceutically acceptable metal saltsor--optionally alkylated--ammonium salts.

Examples of such salts include inorganic and organic acid addition saltssuch as hydrochloride, hydrobromide, sulphate, phosphate, acetate,phthalate, fumarate, maleate, citrate, lactate, tartrate, oxalate, orsimilar pharmaceutically acceptable inorganic or organic acid additionsalts, and include the pharmaceutically acceptable salts listed inJournal of Pharmaceutical Science, 66, 2 (1977) which are herebyincorporated by reference.

In a preferred embodiment of the invention C₁₋₄ -alkyl is methyl orethyl, C₁₋₄ -alkenyl is ethylidene, C₁₋₄ -alkoxy is methoxy or ethoxy,and X includes methoxy, ethoxy, isopropoxy or n-propoxy, and n includes2, 3 or 4.

The compounds of formula I have a greater lipophilicity--and thus agreater availability to the brain--than the parent compounds without theN-substituent (i.e. nipecotic acid and guvacine).

It has been demonstrated that the novel compounds of formula I whichinhibit the uptake of GABA from the synaptic cleft possess usefulpharmacological properties in the central nervous system, in that theycause a selective enhancement of GABA'ergic activity. Compounds offormula I may be used to treat for example, pain, anxiety,extrapyrimidinal dyskinesia, epilepsy and certain muscular and movementdisorders. They are also useful as sedatives, hypnotics andantidepressants.

The compounds of formula I are prepared by the following methods:##STR2##

A compound of formula II wherein A and n are as defined above and Y is asuitable leaving group such as halogen, p-toluene sulphonate or mesylatemay be reacted with an azaheterocyclic compound of formula III whereinR¹, R² and X are as defined above. This alkylation reaction may becarried out in a solvent such as acetone, dibutylether, 2-butanone,tetrahydrofuran, methylisobutylketone or toluene in the presence of abase e.g. potassium carbonate and a catalyst, e.g. an alkali metaliodide at a temperature up to reflux temperature for the solvent usedfor e.g. 1 to 120 h. If esters have been prepared in which X is alkoxy,compounds of formula I wherein X is OH may be prepared by hydrolysis ofthe ester group, preferably at room temperature in a mixture of anaqueous alkali metal hydroxide solution and an alcohol such as methanolor ethanol, for example, for about 0.5 to 6 h. ##STR3##

A compound of formula IV wherein A is as defined above, may be reactedwith a compound of formula V wherein R¹, R², n and X are as definedabove and Z is a suitable leaving group such as halogen, p-toluenesulphonate or mesylate. This alkylation reaction may be carried out in asuitable solvent such as dibutylether, 2-butanone, tetrahydrofuran,methyl-isobutylketone or toluene in the presence of a base e.g.potassium carbonate or sodium hydride at a temperature up to refluxtemperature for the solvent used for e.g. 1 to 120 h. If esters havebeen prepared in which X is alkoxy, compounds of formula I wherein X isOH may be prepared by hydrolysis of the ester group, preferably at roomtemperature in a mixture of an aqueous alkali metal hydroxide solutionand an alcohol such as methanol or ethanol, for example, for about 0.5to 6h.

Compounds of formula II, III and IV may readily be prepared by methodsfamiliar to those skilled in the art. Compounds of formula V may beprepared according to the procedure described in U.S. Pat. No.5,071,859.

Under certain circumstances it may be necessary to protect theintermediates used in the above methods e.g. a compound of formula IIIor V with suitable protecting groups. The carboxylic acid group can, forexample, be esterified. Introduction and removal of such groups isdescribed in "Protective Groups in Organic Synthesis" T. W. Greene andP. G. M. Wuts, 2ed. (John Wiley, 1991).

Pharmacological Methods

Values for in vitro inhibition of [³ H]-GABA uptake for the inventioncompounds were assessed essentially by the method of Fjalland (ActaPharmacol. Toxicol. 1978, 42, 73-76).

Male wistar rat cortical tissue was gently homogenized by hand using aglass/PTFE homogenizer in 10 volumes of 0.32M sucrose. Incubation wasperformed in a 40 mM tris HCl buffer (pH 7.5 at 30° C.) containing 120nM NaCl, 9.2 nM KCl, 4 mM MgSO₄, 2.3 nM CaCl₂ and 10 mM glucose, for 60minutes at 30° C.

Values for inhibition of GABA uptake for some representative compoundsare recorded in Table I.

                  TABLE I                                                         ______________________________________                                        Inhibition of [.sup.3 H]-GABA uptake                                          Example no.   IC.sub.50 (μM) in vitro                                      ______________________________________                                        1             64                                                              2             24                                                              3             6.7                                                             4             5.6                                                             5             5.6                                                             ______________________________________                                    

For the above indications the dosage will vary depending on the compoundof formula I employed, on the mode of administration and on the therapydesired. However, in general, satisfactory results are obtained with adosage of from about 0.5 mg to about 1000 mg, preferably from about 1 mgto about 500 mg of compounds of formula I, conveniently given from 1 to5 times daily, optionally in sustained release form. Usually, dosageforms suitable for oral administration comprise from about 0.5 mg toabout 1000 mg, preferably from about 1 mg to about 500 mg of thecompounds of formula I admixed with a pharmaceutical carrier or diluent.

The compounds of formula I may be administered in pharmaceuticallyacceptable acid addition salt form or where possible as a metal or alower alkylammonium salt.

This invention also relates to pharmaceutical compositions comprising acompound of formula I or a pharmaceutically acceptable salt thereof and,usually, such compositions also contains a pharmaceutical carrier ordiluent. The compositions containing the compounds of this invention maybe prepared by conventional techniques and appear in conventional forms,for example capsules, tablets, solutions or suspensions.

The pharmaceutical carrier employed may be a conventional solid orliquid carrier. Examples of solid carriers are lactose, terra alba,sucrose, talc, gelatin, agar, pectin, acacia, magnesium stearate andstearic acid. Examples of liquid carriers are syrup, peanut oil, oliveoil and water.

Similarly, the carrier or diluent may include any time delay materialknown to the art, such as glyceryl monostearate or glyceryl distearate,alone or mixed with a wax.

If a solid carrier for oral administration is used, the preparation canbe tabletted, placed in a hard gelatin capsule in powder or pellet formor it can be in the form of a troche or lozenge. The amount of solidcarrier will vary widely, but will usually be from about 25 mg to about1 g. If a liquid carrier is used, the preparation may be in the form ofa syrup, emulsion, soft gelatin capsule or sterile injectable liquidsuch as an aqueous or non-aqueous liquid suspension or solution.

Generally, the compounds of this invention are dispended in unit dosageform comprising 50-200 mg of active ingredient in or together with apharmaceutically acceptable carrier per unit dosage.

The dosage of the compounds according to this invention is 1-500 mg/day,e.g. about 100 mg per dose, when administered to patients, e.g. humans,as a drug.

A typical tablet, which may be prepared by conventional tablettingtechniques contains:

    ______________________________________                                        Core:                                                                         Active compound (as free compound                                                                    100       mg                                           or salt thereof)                                                              Colloidal silicon dioxide (Aerosil ® )                                                           1.5       mg                                           Cellulose, microcryst. (Avicel ® )                                                               70        mg                                           Modified cellulose gum (Ac-Di-Sol ® )                                                            7.5       mg                                           Magnesium stearate                                                            Coating:                                                                      HPMC            approx.    9         mg                                       *Mywacett ® 9-40 T                                                                        approx.    0.9       mg                                       ______________________________________                                         *Acylated monoglyceride used as plasticizer for film coating.            

The route of administration may be any route, which effectivelytransports the active compound to the appropriate or desired site ofaction, such as oral or parenteral e.g. rectal, transdermal,subcutaneous, intravenous, intramuscular or intranasal, the oral routebeing preferred.

EXAMPLES

The process for preparing compounds of formula I is further illustratedin the following examples which however are not to be construed aslimiting.

Hereinafter, TLC is thin layer chromatography and THF istetrahydrofuran, CDCl₃ is deuterio chloroform and DMSO-d₆ ishexadeuterio dimethylsul-foxide. The structures of the compounds areconfirmed by either elemental analysis or NMR, where peaks assigned tocharacteristic protons in the title compounds are presented whereappropriate. NMR shifts (δ) are given in parts per million (ppm). M.p.is melting point and is given in ° C. Column chromatography was carriedout using the technique described by W. C. Still et al, J. Org. Chem.1978, 43, 2923-2925 on Merck silica gel 60 (Art. 9385). Compounds usedas starting materials are either known compounds or compounds which canreadily be prepared by methods known per se.

Example 1

(R)-1-(2-Phenoxyethyl)-3-piperidinecarboxylic acid hydrochloride

A mixture of 2-phenoxyethylbromide (20 g, 100 mmol),(R)-3opiperidine-carboxylic acid ethyl ester (34 g, 112 mmol), potassiumcarbonate(41 g, 298 mmol) and methyl isobutylketone (200 ml) was heatedat reflux overnight. The reaction mixture was allowed to cool and thenfiltered. The solvent was evaporated from the filtrate in vacuo and theresidue was purified by column chromatography on silica gel (800 g,heptane/ethyl acetate =4/1) to give 17.1 g of(R)-1-(2-phenoxyethyl)-3-piperidine- carboxylic acid ethyl ester as anoil.

The above ester (3.5 g, 13 mmol) was dissolved in ethanol (35 ml) and 4Nsodium hydroxide (3.2 ml) was added. The mixture was stirred at ambienttemperature overnight. The reaction mixture was diluted with water and4M hydrochloric acid (6.3 ml) was added. The mixture was concentrated invacuo and dichloromethane (50 ml) and acetone were added to the residue.The mixture was concentrated in vacuo to give a solid residue which washeated at reflux with acetone (500 ml). The mixture was filtered whilestill hot and the filtrate was left overnight for crystallisation. Thesolid which formed was isolated by filtration and dried to give 1.0 g ofthe title compound as a solid.

M.p. 169°-170° C. Calculated for C₁₄ H₁₉ NO₃.HCl:

C, 58.8%; H, 7.1%; N, 4.9%; Found:

C, 58.8%; H, 7.2%; N, 4.8%.

Example 2

(R)-1-(4-Phenoxy-1-butyl)-3-piperidinecarboxylic acid hydrochloride

A mixture of 4-phenoxy-1-butylbromide (10 g, 44 mmol),(R)-3-piperidine-carboxylic acid ethyl ester (15 g, 44 mmol), potassiumcarbonate (18 g, 131 mmol) and methyl isobutylketone (100 ml) was heatedat reflux overnight. The reaction mixture was allowed to cool and thenfiltered. The solvent was evaporated from the filtrate in vacuo and theresidue was purified by column chromatography on silica gel (300 g,heptane/ethyl acetate=4/1) to give 12.1 g of(R)-1-(4-phenoxy-1-butyl)-3-piperidinecarboxylic acid ethyl ester as anoil.

The above ester (3.5 g, 11.5 mmol) was dissolved in ethanol (35 ml) and4N sodium hydroxide (5.7 ml) was added. The mixture was stirred atambient temperature overnight. The reaction mixture was diluted withwater and 4M hydrochloric acid (11.5 ml) was added. The mixture wasconcentrated in vacuo and dichloromethane (50 ml) and acetone were addedto the residue. The mixture was concentrated in vacuo to give a residuewhich was heated at reflux with acetone (700 ml). The mixture wasfiltered while still hot and the filtrate was left for crystallisation.The solid which formed was isolated by filtration and dried to give 1.9g of the title compound as a solid.

M.p. 176°-177° C. Calculated for C₁₆ H₂₃ NO₃ HCl:

C, 61.2%; H, 7.7%; N, 4.5%; Found:

C, 61.4%; H, 7.9%; N, 4.5%.

Example 3

(R)-1-(2-(2-Benzylphenoxy)ethyl)-3-piperidinecarboxylic acidhydrochloride

Sodium hydride (0.8 g, 20 mmol, 60% oil dispersion) was addedportionwise to a stirred solution of 2-benzylphenol (1.8 g, 10 mmol) intoluene (30 ml) placed under an atmosphere of nitrogen. The mixture wasstirred for 30 minutes and (R)-1-(2-bromoethyl)-3-piperidinecarboxylicacid ethyl ester hydrobromide (3.5 g, 10 mmol, EP 374801) was addedportionwise. The reaction mixture was stirred for 2 h at ambienttemperature and water (50 ml) was added. The phases were separated andthe organic phase was extracted with a 10% citric acid solution (200ml). This acidic solution was extracted with a small portion of tolueneand the organic extracts were discarded. To the acidic aqueous phase 4Nsodium hydroxide was added until pH 7-8 and the mixture was extractedwith ethyl acetate (150 ml). The organic extract was dried (Na₂ SO₄) andthe solvent was evaporated in vacuo to give 1.7 g of(R)-1-(2-(2-benzylphenoxy)ethyl)-3-piperidine-carboxylic acid ethylester as an oil.

The above ester (1.7 g, 4.6 mmol) was dissolved in ethanol (10 ml) and4N sodium hydroxide (3.5 ml) was added. The mixture was stirred atambient temperature for 5 h. Excess concentrated hydrochloric acid wasadded followed by dichloromethane (300 ml). The phases were separatedand the organic phase was dried (Na₂ SO₄). The solvent was evaporated invacuo to give a foamy residue which was dissolved in acetone (15 ml).The solid which formed was isolated by filtration and dried to give 1.3g of the title compound as a solid.

M.p. 165°-167° C. Calculated for C₂₁ H₂₅ NO₃.HCl:

C, 67.1%; H, 7.0%; N, 3.7%; Found:

C, 66.9%; H, 7.0%; N, 3.4%.

Example 4

(R)-1-(2-(3-Phenylphenoxy)ethyl)-3-piperidinecarboxylic acidhydrochloride

Sodium hydride (0.46 g, 11.6 mmol, 60% oil dispersion) was addedportionwise to a stirred solution of 3-hydroxybiphenyl (0.99 g, 5,8mmol) in toluene (30 ml) placed under an atmosphere of nitrogen. Themixture was stirred for 30 minutes and(R)-1-(2-bromoethyl)-3-piperidinecarboxylic acid ethyl esterhydrobromide (2.0 g, 5.8 mmol, EP 374801) was added portionwise. Thereaction mixture was stirred overnight at ambient temperature and waterwas added (50 ml). The phases were separated and the aqueous phase wasextracted with toluene (20 ml). The solvent was evaporated in vacuo fromthe combined organic phases to give a residue which was dissolved inethyl acetate (100 ml). Water (50 ml) was added and pH was adjusted to 4with a 34% tartaric acid solution. The phases were separated and theorganic phase extracted with 34% tartaric acid (2×5 ml). To the combinedaqueous phases was added ethyl acetate (30 ml) and pH was adjusted to7.5 with 2N sodium hydroxide. The organic phase was washed with brine(10 ml) and dried (Na₂ SO₄). The solvent was evaporated in vacuo to give1.5 g of (R)-1-(2-(3-Phenylphenoxy)ethyl)-3-piperidinecarboxylic acidethyl ester as an oil.

The above ester (1.4 g, 4 mmol) was dissolved in ethanol (30 ml) and 4Nsodium hydroxide (4.5 ml) was added. The mixture was stirred at ambienttemperature overnight. The reaction mixture was concentrated in vacuo togive a residue to which dichloromethane (175 ml) was added. The mixturewas placed on an icebath and concentrated hydrochloric acid (2.1 ml) wasadded. The phases were separated and the organic phase was dried (Na₂SO₄). The solvent was evaporated in vacuo to give a residue which wasdissolved in a mixture of dichloromethane (175 ml) and a small portionof water. The phases were separated and the organic phase was dried (Na₂SO₄). The solvent was evaporated in vacuo to give 0.4 g of the titlecompound as an oil.

¹ H NMR (DMSO-d₆) δ 4.55 (brs, 2H).

Example 5

(R)-1-(2-(2-Phenylphenoxy)ethyl)-3-piperidinecarboxylic acidhydrochloride

A mixture of 2-hydroxybiphenyl (3.0 g, 17.6 mmol),(R)-1-(2-bromoethyl)-3-piperidinecarboxylic acid ethyl esterhydrobromide (6.1 g, 17.6 mmol, EP 374801), potassium carbonate (9.7 g,71 mmol) and methyl isobutylketone (50 ml) was heated at reflux for 22h. The reaction mixture was allowed to cool, diluted with methylisobutylketone and filtered. The solvent was evaporated in vacuo and theresidue was purified by column chromatography (heptane/ethylacetate=2/3) to give 2.7 g of (R)-1-(2-(2-phenylphenoxy)ethyl)-3-piperidinecarboxylic acid ethyl ester as an oil.

The above ester (2.0 g, 5.7 mmol) was dissolved in ethanol (25 ml) and4N sodium hydroxide (6.4 ml) was added. The mixture was stirred atambient temperature for 3 h. Excess concentrated hydrochloric acid wasadded followed by a small portion of water. The mixture was concentratedin vacuo and dichloromethane (100 ml) and water (25 ml) were added. Thephases were separated and the organic phase was dried (Na₂ S₄). Thesolvent was evaporated in vacuo to give a solid residue which wasrecrystallised from acetone to give 1.2 g of title compound as a solid.

M.p. 171°-172° C. Calculated for C₂₀ H₂₃ NO₃.HCl:

C, 66.4%; H, 6.7%; N, 3.9%; Found:

C, 66.4%; H, 6.8%; N, 3.7%.

We claim:
 1. A compound of formula I ##STR4## wherein A is a saturatedor unsaturated five or six-membered carbocyclic ring substituted with(a) phenyl or benzylidene, each of which is optionally substituted withhalogen, C₁₋₄ -alkyl, C₁₋₄ -alkoxy or trifluoromethyl; (b) C₁₋₄ -alkylsubstituted with phenyl or (c) C₁₋₄ -alkenyl substituted with phenyl;wherein the saturated or unsaturated five or six-membered carbocyclicring is optionally fused with a benzo ring;R¹ and R² are hydrogen orform a bond; X is hydroxy or C₁₋₄ -alkoxy; n is 1, 2, 3, 4 or 5; or apharmaceutically acceptable salt thereof.
 2. The compound according toclaim 1, wherein R¹ and R² form a bond.
 3. The compound according toclaim 1, wherein the saturated or unsaturated five or six-memberedcarbocyclic ring is fused with a benzo ring.
 4. The compound accordingto claim 1, wherein A is a phenyl ring which is optionally substituted.5. The compound according to claim 4, wherein the phenyl ring is fusedwith a benzo ring.
 6. The compound according to claim 4, wherein R¹ andR² form a bond.
 7. The compound according to claim 1 whichis(R)-1-(2-(2-Benzylphenoxy)ethyl)-3-piperidinecarboxylic acid or apharmaceutically acceptable salt thereof.
 8. The compound according toclaim 1 which is(R)-1-(2-(3-Phenylphenoxy)ethyl)-3-piperidinecarboxylicacid or a pharmaceutically acceptable salt thereof.
 9. The compoundaccording to claim 1 whichis(R)-1-(2-(2-Phenylphenoxy)ethyl)-3-piperidinecarboxylic acid or apharmaceutically acceptable salt thereof.
 10. A pharmaceuticalcomposition comprising a compound according to claim 1 together with apharmaceutically acceptable carrier or diluent.
 11. The pharmaceuticalcomposition according to claim 10, wherein the compound is present in anamount between 0.5 mg and 1000 mg per unit dose.
 12. A method oftreating a central nervous system ailment related to GABA uptake in asubject in need of such treatment comprising administering to saidsubject an effective amount of a compound according to claim
 1. 13. Amethod of treating a central nervous system ailment related to GABAuptake in a subject in need of such treatment comprising administeringto said subject a pharmaceutical composition according to claim 10.